Why is he doing this to me for..

I’m with my bf for a year. Him & his ex were together for 3 years and had a apartment and a promise ring (even though he says it wasn’t one) and a bank account, phone together you name it. She left him. But he says he hates her so much and he doesn’t love her and stopped while dating her etc. But lately I’m having doubts. I know shes happy with someone else, having a baby; and wants nothing to do with him let alone talk to us because she stopped with us. But my boyfriend will mention stuff they had and I know they had it together and it’s getting to me. For instance I said about how I have to go to the bank. He said why don’t you go to wells fargo it’s the best bank ever (he had that bank with her). He’ll say how much he misses the dog they had. And we’ll go to restaurants like applebee’s and places they went and then he’ll say it. I’m so lost and confused. When he does this he puts it on me and is like it’s your fault. But me and him don’t even live together or have any of that stuff going on a year and a half now and he’ll mention stuff they had and he only had while with her and it’s freaking me out because I had a two year relationship before, and I don’t call out stuff we had together. I feel like he’s making me go insecure and crazy 😞 what would y’all do